feat: cache lesson content for instant restore on reload

Store lesson title, description, and task in localStorage after each
lesson load. On page reload, immediately restore the cached content
to avoid showing "Loading..." placeholder text.

src/app.js

@@ -205,6 +205,31 @@ function saveUserSettings() {
 	localStorage.setItem("codeCrispies.settings", JSON.stringify(state.userSettings));
 }
 
+// ================= LESSON CACHE =================
+
+function restoreLessonCache() {
+	try {
+		const cached = localStorage.getItem("codeCrispies.lessonCache");
+		if (cached) {
+			const data = JSON.parse(cached);
+			if (data.moduleTitle && elements.moduleName) {
+				elements.moduleName.textContent = data.moduleTitle;
+			}
+			if (data.lessonTitle && elements.lessonTitle) {
+				elements.lessonTitle.textContent = data.lessonTitle;
+			}
+			if (data.lessonDescription && elements.lessonDescription) {
+				elements.lessonDescription.innerHTML = data.lessonDescription;
+			}
+			if (data.taskInstruction && elements.taskInstruction) {
+				elements.taskInstruction.innerHTML = data.taskInstruction;
+			}
+		}
+	} catch (e) {
+		// Ignore cache errors
+	}
+}
+
 // ================= MODULE INITIALIZATION =================
 
 async function initializeModules() {
@@ -406,6 +431,21 @@ function loadCurrentLesson() {
 	requestAnimationFrame(() => {
 		elements.editorSection?.classList.remove("transitioning");
 	});
+
+	// Cache lesson display data for instant restore on reload
+	try {
+		localStorage.setItem(
+			"codeCrispies.lessonCache",
+			JSON.stringify({
+				moduleTitle: engineState.module?.title,
+				lessonTitle: lesson.title,
+				lessonDescription: lesson.description,
+				taskInstruction: lesson.task
+			})
+		);
+	} catch (e) {
+		// Ignore storage errors
+	}
 }
 
 // ================= LIVE PREVIEW =================
@@ -603,6 +643,9 @@ function init() {
 
 	loadUserSettings();
 
+	// Restore cached lesson content immediately to avoid "Loading..." flash
+	restoreLessonCache();
+
 	// Initialize CodeMirror editor
 	initCodeEditor();